Bailey Davis can thank her baby daughter for giving her first-hand experience with rotavirus, which causes severe nausea, vomiting and diarrhea. Davis had been studying rotavirus as part of her master’s degree in environmental biology when her daughter contracted the virus at daycare and passed it on to her. “It was terrible,” says Davis. “It’s not something I would wish on my worst enemy.”
Those most at risk of infection include people with compromised immune systems, children under five and the elderly. Although most people develop immunity to rotavirus after exposure, “rotavirus is incredibly infectious,” says Davis. “As little as one infectious viral particle can cause illness in a person.”
Working with School of Environmental Sciences professors Marc Habash and Steven Liss (now vice-principal of research at Queen’s University), Davis recently completed her master’s thesis on detection of human rotavirus in drinking water treatment plant influents, or water that enters the facility from lakes and rivers. Along with the Drinking Water Research Group at the University of Toronto, she measured rotavirus found in southern Ontario surface water as part of a quantitative microbial risk assessment. Eight drinking water treatment plants participated in the study.
Although rotavirus poses no risk to the environment, “it’s a public health threat,” says Davis, adding that rotavirus is often found in waste water. Treated less thoroughly than drinking water, waste water may still contain harmful viruses, she says. “Oftentimes these are sources for drinking water. Different waste water treatment plants have different levels of treatment. It all depends on the plant itself.”
As rotavirus carries a negative charge in raw water, Davis used a positively charged water filter to collect the virus as it entered the treatment plants. She then detected the virus using a molecular technique called reverse transcription polymerase chain reaction.
“Viruses are a little more tough to work with,” she says, partly because of their size (70 to 90 nanometres). “With the rise of molecular methods, now it’s becoming much easier to detect and determine what viruses are present.” Previously, enteric viruses were often studied using cell cultures. As viruses aren’t living organisms they need to find a host in the cells of other organisms to replicate. Davis says rotavirus is difficult to study, because it’s not easy to infect cells with the virus (it needs to be treated with trypsin to increase infectivity) or to determine whether the cells are infected.
Viruses consist of DNA or RNA encased in a protein coat called a capsid. Rotavirus has a triple-layer protein coat and a double strand of RNA, which is believed to help the virus resist common disinfection techniques such as chlorination, says Davis. Higher concentrations of chlorine are required to deactivate rotavirus than to kill bacteria. Drinking water treatment facilities also use ultraviolet radiation and ozonation to clean water. “Plants typically don’t use filters, because they clog quite easily and they deal with massive quantities of water.”
Davis says this type of study is the first of its kind in southern Ontario. Previous drinking water studies often focused on bacteria and protozoa such as E. coli, Cryptosporidium and Giardia. “Health Canada is looking at implementing rules and regulations for virus loads in water. They want a four-log (99.99-per-cent) reduction of viruses in drinking water. In order to do that, you need to know how much you are dealing with in the first place.”
Rotavirus A, often found in human waste, is believed to cause 90 per cent of rotavirus infections worldwide. These infections peak in early spring. “Cold weather does help to sustain infectivity.”